如何优化 T-SQL 查询

Question

我正在编写一个 T-SQL 查询，我正在开发电子商务网站，因为我正在使用 4 个主要表：

1. 产品类别
2. 产品
3. OrderLineItem
4. 订购

我的管理部分有一页用于管理订单，现在我想按ProductCategory 过滤，即Order 包含Product（我的productId 在OrderLineItem 表中）与选定的ProductCategory 相关，我通过以下查询执行此操作：

SELECT  
    O.OrderID,O.[OrderDate],O.[StatusID]                          
FROM [Order] O                              
INNER JOIN [Dyve_User] U ON U.[UserID] = O.[UserID]                               
INNER JOIN (SELECT OD.OrderID 
            FROM OrderLineItem OD
            LEFT OUTER JOIN [Product] P ON OD.ProductID = P.ProductID
            LEFT OUTER JOIN [ProductCategory] PC ON PC.CategoryID = P.CategoryID
            WHERE 
               (P.CategoryID = COALESCE(@CategoryID, P.CategoryID)                              
                OR P.CategoryID IN (SELECT CategoryID 
                                    FROM ProductCategory                              
                                    WHERE ParentID = COALESCE(@CategoryID, ParentID)
                                   )
               )                              
           ) AS T  ON O.OrderID = T.OrderID  

我的这个查询返回正确的结果，但是每次查询都会超时，谁能告诉我如何优化这个查询，这样就不会超时了？

以下是表格架构：

CREATE TABLE [dbo].[Order](
[OrderID] [int] IDENTITY(1,1) NOT NULL,
[OrderDate] [datetime] NULL,
[OrderTax] [money] NULL,
[OrderTotal] [money] NULL,
[ShippingCharge] [money] NULL,
[TrackingNumber] [varchar](50) NULL,
[TransactionStatusID] [int] NULL,
[UserID] [int] NULL,
[PromotionCode] [varchar](50) NULL
[ExpiryDate] [datetime] NULL,
[PaymentType] [tinyint] NULL
  CONSTRAINT [Order_PK] PRIMARY KEY CLUSTERED 
  (
[OrderID] ASC
 )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF,          ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
  ) ON [PRIMARY]

产品表：

CREATE TABLE [dbo].[Product](
[ProductID] [int] IDENTITY(1,1) NOT NULL,
[CategoryID] [int] NULL,
[ProductName] [nvarchar](600) NULL,
[ManufacturerID] [int] NULL,
[UnitPrice] [money] NULL,
[RetailPrice] [money] NULL,
[IsOnSale] [bit] NOT NULL,
[ExpiryDate] [datetime] NULL,
[IsElectrical] [bit] NULL,
[IsActive] [bit] NULL,
[ProductType] [int] NULL,
[AllowBackOrder] [bit] NULL
   CONSTRAINT [Product_PK] PRIMARY KEY CLUSTERED 
   (
[ProductID] ASC
    )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF,        ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
   ) ON [PRIMARY]

产品类别表：

CREATE TABLE [dbo].[ProductCategory](
[CategoryID] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](100) NOT NULL,
[Description] [nvarchar](max) NULL,
[ParentID] [int] NULL,
[IsActive] [bit] NULL
    CONSTRAINT [ProductCategory_PK] PRIMARY KEY CLUSTERED 
   (
[CategoryID] ASC
   )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF,        ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
  ) ON [PRIMARY]

OrderLineItem 表：

CREATE TABLE [dbo].[OrderLineItem](
[OrderDetailID] [int] IDENTITY(1,1) NOT NULL,
[OrderID] [int] NOT NULL,
[ProductID] [int] NOT NULL
[TotalPrice] [money] NULL,
[Quantity] [int] NULL,
[Discount] [money] NULL,
[UnitPrice] [money] NULL,
[UserID] [int] NULL,
    CONSTRAINT [OrderLineItem_PK] PRIMARY KEY CLUSTERED 
      (
[OrderDetailID] ASC
   )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF,        ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
   ) ON [PRIMARY]

Answer 1

从以下几点开始：

1. 在连接和位置列上定义索引。
2. 从较小的表加入到较大的表中。

我建议阅读有关性能以及如何查找原因的内容 - 这是一篇关于该主题的好文章：part 1 和 part 2。

Answer 2

这未经测试，所以我不确定它是否仍然符合您对查询的预期。

它将获取具有OrderLineItem 和Product 的Orders 以及等于@CategoryID 的CategoryID 或@CategoryID 的子类别。

SELECT O.OrderID,
       O.[OrderDate],
       O.[StatusID]
FROM   [Order] AS O
WHERE  O.OrderID IN (SELECT OD.OrderID
                     FROM   OrderLineItem AS OD
                            INNER JOIN Product AS P
                              ON OD.ProductID = P.ProductID
                            INNER JOIN (SELECT PC.CategoryID
                                        FROM   ProductCategory
                                        WHERE  ParentID = @CategoryID
                                        UNION ALL
                                        SELECT @CategoryID) AS C
                              ON P.CategoryID = C.CategoryID)

关于性能，您只需对其进行测试即可找到答案。

索引是个好东西，你应该确保你的外键列上有索引。

Answer 3

首先尝试延长超时时间以使其正常工作。比掠夺你的执行计划。将元素较少的表移到联接的左侧。